1. Field of the Invention
The present invention generally relates to an evaporator for cooling units used for refrigerating cycles. More particularly, the present invention relates to an evaporator for cooling units connected in parallel with a plurality of refrigerant passages.
2. Description of Related Art
An evaporator has been devised heretofore for use in cooling units, in which a core composed of stacked two pieces of flat core plates to form a refrigerant passage and a fit are alternatively stacked for a plurality of units. However, the evaporator in this arrangement is uneven in the distribution of refrigerant to each refrigerant passage. In an attempt to solve this problem, an evaporator as disclosed in the Japanese Examined Patent Publication No. 58-41429, for example, is known. In this evaporator, a long and narrow micro-passage working as a fixed throttles is formed at each core plate. Refrigerant condensed into a liquid refrigerant by a condenser is fed into the evaporator as it is, and then distributed to each refrigerant passage at an even flow rate with the fixed throttles of each core so that the pressure of the refrigerant is reduced thereby.
On the other hand, an evaporator provided with a heat exchange part for heat exchange between a high-temperature pipe of the receiver outlet side, and a low-temperature pipe between the evaporator and a thermo-sensing tube to minimize the gaseous refrigerant which does not participate in cooling performed in the downstream from a receiver and to increase the effective refrigerant (i.e., supercooling) has been proposed (as disclosed in the Nippondenso Technical Disclosure Bulletin No. 40-076, issued on Mar. 15, 1985).
However, in these conventional evaporators with a fixed throttle, when refrigerant in gas-liquid two phase state flows into the fixed throttle, the even distribution of the refrigerant can not be achieved. Namely, there are two types of fixed throttles; one through which gaseous refrigerant mainly flows, and the other through which liquid refrigerant mainly flows.
Accordingly, it is conceivable that the evaporator with fixed throttles is used for the refrigerating cycle, the refrigerant after the receiver is cooled at the heat exchange part by the low-temperature refrigerant flowed through the evaporator so that the refrigerant is supercooled, whereby the liquid refrigerant is increased to make the distribution of the refrigerant by the fixed throttle more even.
However, when the indoor temperature is higher than the outdoor temperature as it is in the winter season and the temperature of the air to cool the condenser is as low as 0.degree. to 10.degree. C., or when the volume of the refrigerant to be fed into the evaporator is not sufficient due to the insufficient volume of the refrigerant within the receiver as it is in the transient operation state, there are some cases where the temperature at the outlet of the evaporator rose and the cooling of the refrigerant at the heat exchange part was not performed sufficiently. Furthermore, when the temperature of the refrigerant at the outlet of the evaporator is higher than that of the refrigerant flowed through the receiver, there are some cases where the refrigerant flowed through the receiver is evaporated and the performance of the evaporator is substantially reduced.
Moreover, in the above evaporator, the fixed throttles are formed in the two pieces of flat core plates having a recess part. In order to attain an even distribution of the refrigerant, however, the cross-sectional profiles of these fixed throttles must be exactly aligned with one another, otherwise, uneven distribution of the refrigerant may result. For example, if these two flat core plates are connected to each other by brazing, brazing filler metal may flow into the fixed throttles, causing a manufacturing problem in that it is difficult to produce fixed throttles which are exactly aligned with one another.
Accordingly, a primary objective of the present invention is to solve the above problems and provide an evaporator for cooling units which can evenly distribute the refrigerant to each refrigerant passage without causing any performance degradation.